Note to the wise:
If you are upgrading to Mac OS X Mountain Lion, make sure that your copy of VirtualBox is up-to-date. If it isn’t, and if you are running a VBoxHeadless session to start a VM at login, you will be in a boot loop as the Mac will bugcheck and do a soft reboot.
That’s why if you visited my weather website this afternoon and didn’t see up-to-date information - my VBoxHeadless instance running my XP VM (for the Weather Station software) was causing a reboot. All is fixed now. :)